<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>造型函数</title>
</head>
<body>
  <script src="../common/lib/gl-renderer.js"></script>
  <canvas width="512" height="512"></canvas>
  <script>
    const vertex = `
      attribute vec2 a_vertexPosition;
      attribute vec2 uv;

      varying vec2 vUv;

      void main() {
        gl_PointSize = 1.0;
        vUv = uv;
        gl_Position = vec4(a_vertexPosition, 1, 1);
      }
    `;

    const fragment = `
      #ifdef GL_ES
      precision highp float;
      #endif

      varying vec2 vUv;
      uniform float u_k;
      uniform float u_scale;
      uniform float u_offset;

      vec2 polar(vec2 st) {
        return vec2(length(st), atan(st.y, st.x));
      }

      void main() {
        vec2 st = vUv - vec2(0.5);
        st = polar(st);
        float d = u_scale * 0.5 * abs(cos(st.y * u_k * 0.5)) - st.x + u_offset;
        gl_FragColor.rgb = smoothstep(-0.01, 0.01, d) * vec3(1.0);
        gl_FragColor.a = 1.0;
      }
    `;

    const canvas = document.querySelector('canvas');
    const renderer = new GlRenderer(canvas);
    const program = renderer.compileSync(fragment, vertex);
    renderer.useProgram(program);
    renderer.uniforms.u_k = 1.7;
    renderer.uniforms.u_scale = 0.5; // default 1.0
    renderer.uniforms.u_offset = 0.2; // default 0.0

    // setInterval(() => {
    //   renderer.uniforms.u_k += 2;
    // }, 200);

    renderer.setMeshData([{
      positions: [
        [-1, -1],
        [-1, 1],
        [1, 1],
        [1, -1],
      ],
      attributes: {
        uv: [
          [0, 0],
          [0, 1],
          [1, 1],
          [1, 0],
        ],
      },
      cells: [[0, 1, 2], [2, 0, 3]],
    }]);

    renderer.render();
  </script>
</body>
</html>